Ultraviolet-photoemission studies of TlCl

In-situ-prepared TlCl films have been studied with photoemission for photon energies up to 11.8 eV. Photoelectron energy-distribution curves (EDC's) show two strong valence-band density of states at 1.0 and 2.2 eV below the valence-band maximum (VBM) and one weaker piece of structure at 3.4 eV below the VBM. They also suggest a strong conduction-band density of states near 8.1 eV and a minimal density-of-states region 9.0-10.0 eV above the VBM. The valence-band width estimated from the EDC's is 4.0 eV. Comparing these features to theoretical calculations, the relativistic Korringa-Kohn-Rostoker calculation by Overhof and Treusch yields correct valence-band width and gives fair qualitative but not quantitative agreement. The electron escape length for electrons 6.9 to 7.6 eV above the VBM (0-0.7 eV above the photoelectric threshold) is estimated to be 200 Å by photoinjection method. EDC's also exhibit strong temperature dependence. It is suggested that this is due to the dynamic modulation of the orbital hybridization in the valence-band electronic states because of lattice vibrations. It is further suggested that the effect of lattice vibrations on electrons (or vice versa) cannot be treated as a perturbation in the usual electron-phonon interaction approach, and may be responsible for unusual lattice dynamics of TlCl. Exposure of TlCl thin films to ${\mathrm{Cl}}_2$ gas up to 500 langmuirs (at 1 × ${10}^{-8\mathrm{}}$ Torr) at 25 and 50°C yielded no change of EDC's.